Tetrahalogen substituted quinacridones



United States Patent TETRAHALOGEN SUBSTITUTED QUINACRIDONES William S.Struve, Chatham, N. 5., assignor to E. I. du 'Pont de Nemours andCompany, Wiimington, Del.,

acorporation of Delaware N Drawing. Application January 4, 1956 SerialNo. 557,245

'11 Claims. (Cl. 260-279) This invention relates to the preparation ofnew colored pigments comprising symmetrical tetrahalogen substitutedlinear quinacridones.

In my co-pending application, Serial No. 523,922, filed July 22,l955,there is disclosed the method of preparing linear quinacridones ofthe following structural formula:

\I I 6 N Formula 1 I! 0 i i X 11 1a\-' 12 14 5 6 N K II I X 0 H Formula2 where X is selected from the group consisting of chlorine, bromine,fluorine and iodine. As can be readily seen, the above formula is linearin structure, and the term, quinacridone or dihydro-quinacridone, asused in the ensuing description and claims refers to this linearstructure. It is'also pointed out that'the two halogens on each of theendrings are so 'posiitoned .as to form a symmetrical molecule. Thecompounds of this structure have'been foundto be useful as pigmentsexhibiting a yellower shade than "the compounds of'my above-mentionedco-pending application.

It is an object of this invention to provide anovel process for"preparing a new and useful class of compounds known as symmetricaltetrahalogen substituted linear quinacridones. It is afurther object toprovide a novel process for preparing a new and useful class ofcompounds known as symmetrical tetrahalogen substituted lineardihydroquinacridones. It is a still further object ofsthistinvention toprovide symmetricaltetrahalogen substituted linear .quinacridonepigments iranging, in the hue from .orange toyellowish. red, andpossessing a high: degree of brightness,:lightfastness, durability andfreedom from bleed .in solvents and chemical reagents.

. ,These and other objectsofthis invention are :accom- Patented Jan. 28,1958 plished by condensing under non-oxidizing conditions, such as anitrogen atmosphere, a dialkyl succinyl succinate with an excess of adihaloaniline in the presence of an acid catalyst. Various solvents maybe used for this condensation. Denatured ethyl alcohol is preferredbecause it is readily available and relatively economical. After thecondensation step, the'reaction mixture is neutralized, and thecondensed product recovered. The compound resulting from thiscondensation is a dialkyl tetrahalo-2,5,-

dianilino-3,6-dihydroterephthalate which may be represented bythefollowing structural formula:

COOR X H N H3 H2 N H X X OOOR Formula 3 where R is an alkyl group and Xis a halogen. Cyclization of the above compound to the compound shown inFormula 4 is "then brought about by heating it in a high boilingsolvent, such as a eutectic mixture of 23.5% by weight of biphenyl and76.5% by weight of diphenyl oxide. This pyrolysis proceeds most readilynear the boiling point of the eutectic mixture, and it should be carriedout under a non-oxidizing atmosphere such as a blanket of nitrogen.Alcohol is a by-product since the ester splits, and the R0 group takeson a hydrogen liberated by the formation of the new rings. The compoundrecovered from the cyclization reaction is a tetrahalo-6,13-dihydro-quinacridone which is represented by the following structuralformula:

0 X H Hz ll X N\ C 0 N X [I H2 H X Formula 4 where X is a'halogen.

The above compound is then oxidized with a mild oxidizing agent therebyremoving a hydrogen atom from both the 6 and 13 positions to form alinear tetrahaloquinacridone as shown in Formula 2.

The final products obtained by the above-described process are highlycolored, and they are suitable as pigments. For this purpose a smallparticle size is contemplated and tetrahalogen substituted quinacridoneshaving a. surface area greater than about 60 square meters per gram (as"measured by the nitrogen absorption method of Emmett described inAdvances in Colloid Science, vol. 1, 1-942) willbe found suitable.

T he tetrahalogen substituted dihydro-quinacridones and guinacridones ofthis invention may be represented by the following structural formula:

where n is an integer of from '1 to 2 and X is a halogen selected fromthe group consisting of chlorine, fluorine, bromine, and iodine. If n isl, the structure represents quinacridone, and as will be seen fromFormula 2, it is not customary to show the single hydrogen attached tothe ring when depicting the specific formula for this compound. Itshould also be noted that the compounds of this invention aresymmetrical with respect to the position of the halogen atoms on the endrings.

In the preferred embodiment of this invention, 2,4-dichloroaniline iscondensed with diethyl succinyl succinate by refluxing in ethyl alcoholin the presence of a small amount of the corresponding anilinehydrochloride as a catalyst. A large excess of 2,4-dichloroaniline isused and the operation is carried out under a blanket of an inert gas,such as nitrogen. After the condensation step is concluded, the reactionmixture is neutralized and the condensed ester is recovered. Thecompound resulting from this condensation is diethyltetrachloro-2,5-dianilino- 3,6-dihydroterephthalate and cyclization ofthis compound is then brought about by heating it in a high boilingsolvent such as Dowtherm A (eutectic mixture of 23.5% by weight ofbiphenyl and 76.5% by weight of diphenyl oxide). This pyrolysis proceedsmost readily near the boiling point of the Dowtherm A and should also becarried out under a blanket of an inert gas; e. g., nitrogen. After theheating, 2,4,9,11-tetrachloro-6,13-dihydroquinacridone is recovered fromthe Dowtherm A, and it is oxidized to the quinacridone compound byreacting with a mild oxidizing agent such as sodiumm-nitrobenzenesulfonate in an alkaline alcoholic medium at a temperaturein the general vicinity of 100 C.

Other tetrachloroquinacridones may be similarly prepared, and thefollowing table gives the compounds which are formed from the variousisomers of dichloroaniline.

TABLE I Diehloroanilines Tetracchloroquinggrldone ompoun2,3-dich1oroaniline 2,4-dichloroaniline 2, 5-dich1oroaniline.3,4-dichloroaniline.

o 3,5-dichloroaniline.

3,4,10,1l-tetrachloroquinacridonc. 2,4,9,ll-tetrachloroquinacridone.1,4,8,ll-tetrachloroquinacridone. 2,3,9,IO-tetrachloroquinacridone.1,2,8,Q-tetrachloroquinacridone. 1,3,8,IO-tetrachloroquinacridone.

A mixture of 200 parts of 2,4-dichloroaniline, 149 parts of diethylsuccinyl succinate, 20 parts of 5 N HCl, and 2,900 parts of denaturedethyl alcohol (Formula 2B-- denatured with benzene, Langes Handbook ofChemistry, 6th ed. (1946)) was heated with stirring under reflux (about80 C.) in an atmosphere of nitrogen for about nine hours. 50 parts of a2 N solution of sodium carbonate was then added, and the mixture wascooled to approximately room temperature with stirring. It was thenfiltered and the product was washed with alcohol and dried giving 261parts of diethyl 2',4',2",4"-tetrachloro-Z,5-dianilino-3,6-dihydroterephthalate which is assigned thefollowing formula:

E N Hz C1 C]- H N-- COOCZHI 01 Formula 6 It is possible to havetautomerism in this type of compound with the double bond of the centerring shifting and the hydrogen on the nitrogen atoms becoming attachedto said ring. However, the above formula is considered to be the correctmethod of illustrating the compound structure of the terephthalateintermediate of this invention.

45 parts of the above dianilino ester is then added to 450 parts ofDowtherm A (a mixture of 23.5% by weight of biphenyl and 76.5% by weightof diphenyl oxide) and the mixture is heated at the boiling point of theDowtherm A for about 1% hours under an atmosphere of nitrogen. Theresulting slurry is cooled with agitation to about room temperature. Itis then filtered, and the cake is washed with alcohol untilsubstantially free of Dowtherm A. After drying, there is obtained 27parts of 2,4,9,11-tetrachloro-6,l3-dihydroquinacridone of the followingformula:

01 H 0 i E t 11 13 10 12 14 c1 Formula 7 190.5 parts of thistetrachlorodihydro-quinacridone, 3,900 parts of ethylene glycol, 500parts of 30% sodium hydroxide solution and 190.5 parts of sodiumm-nitrobenzenesulfonate are mixed and heated with agitation at C. forabout 5 hours. The resulting slurry is diluted with 1,500 parts of coldwater, and the solid is separated by filtration, washed alkali free withwater, and dried to give an orange colored powder of the followingformula:

01 0 I r t O: U cl 1. o o N ll H 0 01 Formula 8 The product is purifiedby dissolving it in ten parts of 100% sulfuric acid, and thenprecipitating it by diluting the resulting solution with water to 85%sulfuric acid. The precipitate is filtered off and washed acid free withwater, thus giving the orange colored material in a purified and highlycrystalline form.

To have utility as a pigment, it is necessary that thetetrachloroquinacridone obtained above be converted to a small particlesize. As one etfective means of accomplishing this end, ten parts of thetetrachloroquinacridone is mixed with parts of salt and two parts ofxylene and ground in a ball mill for about 72 hours. After separatingthe resulting orange colored powder from the grinding balls, it isextracted with a dilute (about 5%) sulfuric acid solution at the boil,filtered, washed acid-free and dried to give a bright orange pigment ofexcellent lightfastness and free from any tendency to bleed in water,organic solvents, dilute acid or dilute alkalies.

This pigment dissolves in concentrated sulfuric acid to give a deepviolet solution from which the original orange pigment is reprecipitatedon drowning in a large volume of water.

Example 11 A mixture of 25.6 parts of diethyl succinyl succinate, 48.6parts of 3,4-dichloroaniline, 560 parts of denatured alcohol (Formula2B) and 6 parts of 5 N HCl is heated with agitation to the boil andmaintained under reflux conditions for about two hours during which anatmosphere of nitrogen is maintained in the flask. 15 parts of a 2 Nsolution of sodium carbonate is then added, and

the flask cooled to about room temperature, and the solid isolated byfiltration, washing with alcohol, and drying to give 54 parts of thedianilino compound which is assigned the following structural formula:

COOOiHa H 01- N H2 01 01- H N- C1 Formula 9 45 parts of this dianilinocompound is mixed with 450 parts of Dowtherm A and heated at the boilingpoint of Dowtherm A in an atmosphere of nitrogen for 1 /2 hours and thencooled to about room temperature. The solid is filtered off, washed withalcohol until substantially free of Dowtherm A and then dried giving25.5 parts of 2,3,9,10-tetrachloro-6,13-dihydro-quinacridone of thefollowing structural formula:

Formula 25 parts of this tetrachlorodihydro-quinacridone, mixed with 480parts of alcohol (Formula 2B), 67 parts of 30% sodium hydroxide solutionand 25 parts of sodium mnitrobenzenesulfonate, is heated to the boilwith agitation for about 4 hours. The solid is then filtered off, washedfree of alkali and dried to give a red solid having the followingstructural formula:

Formula 11 As will be seen from Table I, 3,4-dichloroaniline can formtwo .difierent tetrachloroquinacridones. The quinacridone shown in theabove formula is the one that is believed to predominate in the endproduct of the process. However, it is possible that the end productcould c011 tain some 1,2,8,9-tetrachloroquinacridone.

When dissolved in concentrated sulfuric acid, a violet solution results.The original red colored material may be reprecipitated on drowning thesolution with water. By selecting the proper concentration the coloredmaterial will precipitate before the impurities (this is usually about85% sulfuric acid), and it is possible to use this method to purify theproduct.

To obtain the material in a suitable particle size for use as a pigment,it may be salt milled as described in Example I to give a brilliantyellowish-red pigment of excellent properties with respect to color,lightfastness, and freedom from bleed in various solvents and chemicalagents to which it might be exposed.

Example 111 If 2,5-dichloroaniline is used in the process described inExample I above, the resulting product after salt milling is a brilliantyellowish-red pigment comprising 1,4,8, 1 l-tetrachloroquinacridone.

Example IV The following table summarizes the results obtained by theuse of other dichloroanilines and by the use of various dibromo anddifluoro anilines in a process like that of Example I.

The condensation of dihaloaniline derivatives, such as dichloroaniline,with succinyl succinic ester is acid catalyzed. The catalyst is ineffect a salt of the aniline derivative which is used in the reaction,and it is effectively formed in situ by the addition of a small amountof acid; e. g., HCl, which forms a soluble salt. Other examples ofmaterials suitable for forming the catalyst include HBr, H1, HNO and CHCOOH.

The examples show the use of ethyl alcohol as a solvent for thecondensation. This makes it easy to subsequently filter the end productfrom the solution, and also to further wash with alcohol to effectivelyremove the unreacted dihaloaniline from the mixture. The amount ofsolvent is not critical so long as it keeps the materials in solution. Apreferred amount is from 10 to 40 times the weight of the succinylsuccinic ester. It is also possible and might even be preferred to carryout the condensation in the presence of a high boiling solvent of thetype which might be used to continue the ring closure step. This wouldeliminate the isolation of the terephthalate ester (see Formula 3)formed in the condensation reaction. With this procedure, however, itwould be necessary to remove the excess aniline derivative before thecyclization step. This could be done by such means as vacuumdistillation.

The preferred temperature of the condensation reaction is about C. andit is effective within the range of about 60 to C. At the preferredtemperature the optimum time of reaction is about 2 hours. This may bevaried within the range of about 1 to 6 hours.

The neutralization step subsequent to the completion of the condensationis advantageous to minimize oxidation of thetetrahaloanilino-terephthalate compound which has been formed. Thealkali metal and the alkaline earth metal bicarbonates are the type ofneutralizing agents which are especially suitable. For example, it isconvenient to use sodium bicarbonate or potassium bicarbonate,monosodium phosphate or monocalcium phosphate as a slurry in a smallamount of water.

While the examples have been concerned with the use of diethyl succinylsuccinate it should be understood that corresponding methyl and propylesters can be used. However, if other esters are used, one should usethe corresponding alcohol as a solvent in order to prevent any esterinterchange.

The examples show the use of nitrogen to maintain a non-oxidizingatmosphere. However, the only requirement of the gas used is that it beinert and free from oxygen. Thus, carbon dioxide could be used ifsufficiently pure as well as argon, helium or other inert gases.Nitrogen is preferred because it is readily available at a low cost in apure form, but it is not intended to exclude the use of other gaseswhich would form a shielding atmosphere.

The cyclization of the dianilino compound to the dihydro-quinacridone isconveniently carried out as shown in the examples at the boilingtemperature of Dowtherm A. On the other hand, many other inert liquidsof a suitably high boiling point may be used with equal facility.Examples of such materials include a methyl naphthalene, ,8 methylnaphthalene, biphenyl, diphenyl oxide and min- 7 eral oils boiling aboveabout 250 C. and mixtures of these liquids. The preferred boiling rangefor the inert liquid is from about 240-300 C. In general, thetemperature of the pyrolysis step should be between about 240 and about260 C., and the time may vary from about 45 minutes to about threehours.

The oxidation of the dihydro-quinacridone to quinacridone isconveniently carried out with a mild oxidizing agent such as asulfonated nitrobenzene derivative in the presence of an alkalinealcoholic medium. The examples show the use of a sodium hydroxidesolution in ethylene glycol or ethanol, but other alcoholic solventssuch as methanol, normal propanol, and the various monoethers ofethylene glycol may be used with suitable modifications of the process.In general, it is preferred that the reaction be carried out underalkaline conditions, but the choice of solvent and the choice of agentis not critical. It is possible to carry out the oxidation by simplystirring while bubbling air through the mixture in which thetetrahalodihydro-quinacridone is produced, or a suitable oxidizingmixture may be introduced at this point. Oxidation is evident from themarked change in. color which accompanies the reaction.

The tetrahalogen substituted quinacridones of this invention arepigments of great value showing a brilliant orange to yellowish-redcolor and a very high resistance to fading on exposure to the elements.They also exhibit complete insolubility in the usual solvents of coatingcompositions and the like, as well as insolubility in the ordinary acidsand alkalies to which compositions made from these pigments might beexposed in the normal expected uses. In this range of orange toyellowish-red pigments, there has been a notable lack of productsexhibiting high lightfastness and durability in coating compositions.For this reason, the products of this invention are considered to becapable of filling a long felt need in the pigment industry.

I claim:

1. A new composition of matter comprising a quinacridone selected fromthe group consisting of symmetrical tetrahalo substituteddihydro-quinacridones and symmetrical tetrahalo substituted linearquinacridones of the following structural formula:

where both ns are the same whole number of from 1 to 2 and X is ahalogen selected from the group consisting of fluorine, chlorine,bromine, and iodine, and the substituents X are symmetrical with respectto their positions on the end rings.

2. The composition of claim 1 in which n is 2.

3. The composition of claim 2 in which X is chlorine.

4. A new composition of matter comprising a symmetrical tetrahalosubstituted quinaeridone of the following structural formula:

where X is a halogen from the group consisting of fluorine, chlorine,bromine, and iodine and the substituents X are symmetrical with respectto their positions on the end rings.

5. The composition of claim 4 in which X is chlorine.

6. 2,4,9,1 1-tetrachloroquinacridone.

7. 2,3,9,10-tetrachloroquinacridone.

8. 1,4,8,1 1-tetrachloroquinacridone.

9. 2,4,9, 1 l-tetrabromoquinacridone.

10. A process for preparing a symmetrical tetrahalo substituted linearquinacridone which comprises heating under non-oxidizing conditions adialkyl tetrahalo-2,5- dianilino-3,6-dihydroterephthalate, having from1-3 carbon atoms in the alkyl groups, in an inert high boiling liquid attemperatures ranging from about 240-260 C. thereby obtaining a tetrahalosubstituted linear dihydroquinacridone, separating saiddihydro-quinacridone from the reaction mixture and oxidizing the lattercompound with a mild oxidizing agent to a tetrahaloquinacridone, saidoxidizing agent being selected from the group consistingof'nitrobenzene-m-sodium sulfonate and oxygen.

11. The process of claim 10 in which the dialkyltetrahalo-2,5-dianilino-3,G-dihydroterephthalate is a dialkyltetrachloro-2,5-diani1ino-3,6-dihydroterephthalate, and the high boilingsolvent is a mixture of 23.5% by weight of biphenyl and 76.5% diphenyloxide.

References Cited in the file of this patent UNITED STATES PATENTS Scottet a1. Sept. 15, 1936 OTHER REFERENCES Liebermann: Annalen, v. 518,pages 245-59.

1. A NEW COMPOSITION OF MATTER COMPRISING A QUINACRIDONE SELECTED FROMTHE GROUP CONSISTING OF SYMMETRICAL TETRAHALO SUBSTITUTEDDIHYDRO-QUINACRIDONES AND SYMMETRICAL TETRAHALO SUBSTITUTED LINEARQUINACRIDONES OF THE FOLLOWING STRUCTURAL FORMULA: